Browsing by Author "Singh, Ashutosh"

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A new pyrene-based aggregation induced ratiometric emission probe for selective detections of trivalent metal ions and its living cell application
(2015-02-01)
Singh, Ashutosh
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Singh, Ravinder
;
Shellaiah, Muthaiah
;
Prakash, Epperla Chandra
;
Chang, Huan-Cheng
We synthesize a newly designed pyrene-based fluorescent probe FBP containing a Schiff base and amide linkage as a receptor, which demonstrates selective UV-vis and fluorometric detections of trivalent metal ions in various semi-aqueous solution conditions. Interestingly, by increasing water contents the aggregation induced ratiometric emissions (AIREs) of photoluminescence in FBP solutions (in DMSO/H2O) are enhanced from blue to green due to the excimer formation of the aggregates in water. In addition, the enhanced aggregated ratiometric green fluorescence behaviors of FBP in the presence of trivalent metal ions (Al3+, Fe3+, and Cr3+) are observed in semi-aqueous solutions as well as the solid state, which is well utilized to detect trivalent metal ions in living cells. Further verification of the probe detections, their interactions toward trivalent metal ions are well characterized by the time-resolved photoluminescence (TRPL) of spectroscopic responses as well as theoretical calculations. Therefore, we believe the application of such a new AIRE-based approach is first reported among Schiff base and pyrene-based fluorescentchemo- and bio-sensors. (C) 2014 Elsevier B.V. All rights reserved.
Exploration of Energy Modulations in Novel RhB-TPE-Based Bichromophoric Materials via Interactions of Cu2+ Ion under Various Semiaqueous and Micellar Conditions
(2016-03-16)
Singh, Ravinder
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Dwivedi, Atul Kumar
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Singh, Ashutosh
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Lin, Chien-Min
;
Arumugaperumal, Reguram
Novel bichromophoric materials TR-A and TR-B consisting of an entirely new combination of TPE and RhB units were developed to explore the optimum conditions of energy modulations via pH variation and Cu2+ interaction at various water contents of CH3CN. Interestingly, TR-A and TR-B, at 60 and 70% water contents; respectively, favored the optimum Cu2+-mediated energy modulations from TPE to RhB and thus achieve the brightest orange emissions of free RhB with complete disappearance of aggregation-induced emission (AIE) from TPE. Furthermore, various micellar conditions of triton-X-100, SDS, and CTAB were employed to adjust energy modulations of TR-A and TR-B at high water contents (at 80 and 90%, respectively). The incorporation of RhB into triton-X-100 micellar cavities disrupted AIE from TPE; thus, none of the energy modulations from TPE to RhB occurred even in the presence of Cu2+ ion. Interestingly, the micellar conditions of anionic surfactant (SDS) favored the increased local concentration of Cu2+ ions in the vicinity of scavangable RhB and facilitated the generation of noncyclic free RhB in situ via bright-orange emissions.
Monomeric and aggregation emissions of tetraphenylethene in a photo-switchable polymer controlled by cyclization of diarylethene and solvent conditions
(2017-10-14)
Singh, Ravinder
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Wu, Hsin-Yen
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Dwivedi, Atul Kumar
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Singh, Ashutosh
;
Lin, Chien-Min
A novel photo-switchable polymer P-PHT containing diarylethene (DAE) and tetraphenylethene (TPE) moieties and a triazole linker in the repeating unit was synthesized to study the aggregation-induced emission (AIE) behaviour of TPE with both the open and closed forms of DAE in P-PHT with high water contents. The photo-switching phenomena of DAE (from open to closed forms under UV-irradiation) in P-PHT were prominent in organic solvent (THF), high water contents (at 90% H2O) and acidic conditions. Upon UV-irradiation of P-PHT at 90% water content, the AIE of TPE was completely quenched via an energy transfer event from TPE to cyclized DAE. Interestingly, the rare monomeric emission of TPE was first discovered by the photo-cyclization of DAE in P-PHT compared with the AIE behaviour of TPE with the open form of DAE in P-PHT with AIE favourable conditions of high water content (90% H2O) and acidic conditions.
Naked eye and fluorescent detections of Hg2+ ions and Cysteine via J-aggregation and deaggregation of a perylene bisimide derivative
(2014-04-01)
Fang, Hsiao-Ping
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Shellaiah, Muthaiah
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Singh, Ashutosh
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Raju, Mandapati V. Ramakrishnam
;
Wu, Yen-Hsing
Selective naked eye and fluorescent sensor responses of a 1,6,7,12-tetra(4-tert-butylphenoxy)perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) derivative are reported for the first time toward Hg2+ ions and Cysteine (Cys) via J-aggregation and deaggregation mechanisms. The J-aggregation and deaggregation of PBI induced by Hg2+ and Cys were well established by UV-vis/PL and H-1 NMR titrations. The 1:1 stoichiometry of PBI-Hg2+ and Cys-Hg2+/PBI ensembles were elucidated from the jobs plots based on their UV-vis spectral changes. The linear complex formation by PBI-Hg2+ ensemble was confirmed through FT-IR and H-1 NMR spectral studies and well supported by its reversible nature upon the addition of pentamethyl diethylene triamine (PMDTA). The positive cooperativities of Hg2+ and Cys (with PBI) in PBI-Hg2+ and Cys-Hg2+/PBI ensembles were evidenced from the Hill plots based on their fluorescence binding isotherms. The detection limits of Hg2+ ions and Cys were calculated as 36.6 and 91.3 nM, respectively, by standard deviations and linear fittings of their Stern-Volmer (KSV) constants and relative fluorescence intensity changes, respectively. Furthermore, the sensor properties of PBI were well investigated by KSV constants, pH values, time effects, and time resolved photoluminescence (TRPL) spectra. (C) 2013 Elsevier B.V. All rights reserved.
Novel fluoride-substituted donor/acceptor polymers containing benzodithiophene and quinoxaline units for use in low-band gap solar cells
(2016-09)
Singh, Ashutosh
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Singh, Ravinder
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Lin, Chein-Min
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Pola, Murali Krishna
;
Chang, Chiao-Kai
In this study we used Stille polycondensation to synthesize a series of low-band gap fluoride-substituted conjugated polymers containing electron-donating benzodithiophene (BDT) and electron-accepting quinoxaline (Qx) units, with the latter presenting either two or four fluoride atoms. These donor/acceptor polymers exhibited a broad absorption range (from 300 to 750 nm), with band gap energies of less than 1.20 eV (measured using cyclic voltammetry). Because of their strongly electron-donating thiophene units, the donor/acceptor polymers featuring the more highly fluorinated structures possessed the lowest band gaps (as low as 1.14 eV) and, thus, induced the greatest photovoltaic performance among these tested polymers. The highest power conversion efficiency (2.13%) was obtained from the polymer solar cell featuring an active layer of the polymer PTF2 blended with PC70BM (1:1.5, w/w), with a short-circuit current density, open circuit voltage, and fill factor of 8.7 mA cm(-2), 0.72 V, and 0.34, respectively. (C) 2016 Elsevier Ltd. All rights reserved.
Novel pyrene- and anthracene-based Schiff base derivatives as Cu2+ and Fe3+ fluorescence turn-on sensors and for aggregation induced emissions
(2013)
Shellaiah, Muthaiah
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Wu, Yen-Hsing
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Singh, Ashutosh
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Raju, Mandapati V. Ramakrishnam
;
Lin, Hong-Cheu
Novel pyrene- and anthracene-based Schiff base derivatives P1 and A1 were synthesized via a one-pot reaction and utilized as fluorescence turn-on sensors towards Cu2+ and Fe3+ ions, respectively, and for aggregation induced emissions (AIEs). P1 in CH3CN and A1 in THF illustrated the fluorescence turn-on sensing towards Cu2+ and Fe3+ ions, respectively, via chelation enhanced fluorescence (CHEF) through excimer (P1-P1* and A1-A1*) formation. The 2 : 1 stoichiometry of the sensor complexes (P1 + Cu2+ and A1 + Fe3+) were calculated from Job plots based on UV-Vis absorption titrations. In addition, the binding sites of sensor complexes (P1 + Cu2+ and A1 + Fe3+) were well established from the H-1 NMR titrations and supported by the fluorescence reversibility by adding metal ions and PMDTA sequentially. The detection limits (LODs) and the association constant (K-a) values of P1 + Cu2+ and A1 + Fe3+ sensor responses were calculated by standard deviations, linear fittings and from their fluorescence binding isotherms. More importantly, P1 + Cu2+ and A1 + Fe3+ sensors were found to be active in wide ranges of pHs (1-14 and 2-14, respectively). Moreover, the time effect along with the enhancements of quantum yield (Phi) and time resolved photoluminescence (TRPL) decay constant (tau) towards sensor responses were investigated. Similarly, P1 in CH3CN and A1 in THF showed AIEs by increasing the aqueous media concentration from 0% to 90%, with altered fluorescence peak shifts (red and blue shifts, respectively). As well as tau value enhancements, the Phi values of 0.506 and 0.567 (with 630- and 101-fold enhancements) were acquired for P1 in CH3CN : H2O (20 : 80) and A1 in THF : H2O (40 : 60), respectively.
Novel Water-Soluble Cyclodextrin-Based Conjugated Polymer for Selective Host-Guest Interactions of Cationic Surfactant CTAB and Reverse FRET with Rhodamine B Tagged Adamantyl Guest
(2016-08-09)
Dwivedi, Atul Kumar
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Singh, Ravinder
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Singh, Ashutosh
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Wei, Kung-Hwa
;
Wu, Chu-Ya
A new water-soluble pi-conjugated main-chain polymer P1 bearing a beta-cyclodextrin (beta-CD) pendant was designed and synthesized. The aggregation and disaggregation of P1 generated faded yellow-greenish and bright-yellow emissions, respectively. The inclusion complexation capability of P1 through beta-CD pendant with a cationic surfactant cetyltrimethylammonium bromide (CTAB) guest and associative interactions of P1 with Fe3+ through triazole spacers resulted in significantly enhanced and completely diminished emission profiles of P1 in pure water, respectively. Interestingly, ADRhB as another rhodamine B (RhB) tagged adamantyl guest was transformed into ADRhB(0), i.e., the open form of ADRhB, to generate RhB emission in the presence of Fe3+ ion selectively for the pendent host beta-CD of PI, and the further interaction of.ADRhB(0)/Fe3+ with P1 prevailed a completely quenched RhB emission via the inclusion complexation of adamantyl terminal of ADRhB (0) in beta-CD. Moreover, stronger interactions of CTAB with beta-CD further generated RhB emission of ADRhB(0) even in the presence of acceptor Pl. Finally, a novel beta-CD bearing water-soluble P1 with selective and strong interactions of CTAB toward disaggregation events in pure water, and further electrostatic repulsion and utilization of RhB via RhB-tagged adamantyl guest ADRhB(0) as a donor revealed the reverse fluorescence resonance energy transfer (FRET) process of P1.
Synthesis of fluorinated benzotriazole (BTZ)- and benzodithiophene (BDT)-based low-bandgap conjugated polymers for solar cell applications
(2017-04)
Pola, Murali Krishna
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Boopathi, Karunakara Moorthy
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Padhy, Harihara
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Raghunath, Putikam
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Singh, Ashutosh
A series of donor acceptor (D-A) polymers (P1-P3) based on benzodithiophene (BDT) and electron- accepting benzotriazole (BTZ) units containing thiophene linkers with/without alkyl side-chains were designed and synthesized via Stille coupling polymerization method. The effects of polymers with multiple fluorinated BTZ groups on their thermal, optical, electrochemical, and photovoltaic properties were investigated. These polymers possessed the highest occupied molecular orbital (HOMO) levels ranged -5.38 to -5.6 eV and the lowest unoccupied molecular orbital (LUMO) levels ranged -3.55 to -3.57 eV, which covered broad absorption ranges with low optical bandgaps. The bulk heterojunction (BHJ) polymer solar cell (PSC) devices containing an active layer of D-A polymers blended with different weight ratios of electron-acceptor [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) were explored under 100 mW cm(-2) of AM 1.5 white-light illumination, where the maximum power conversion efficiency (PCE) value of 3% (with J(sc) = 7.70 mA/cm(2), FF = 54.04, and V-oc = 0.72 V) was obtained in the PSC device consisting of polymer P3. (C) 2016 Elsevier Ltd. All rights reserved.
Synthesis of novel platinum complex core as a selective Ag+ sensor and its H-bonded tetrads self-assembled with triarylamine dendrimers for electron/energy transfers
(2014-11-07)
Shellaiah, Muthaiah
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Raju, Mandapati V. Ramakrishnam
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Singh, Ashutosh
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Lin, Hsin-Chieh
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Wei, Kung-Hwa
A novel platinum complex PtC with a tri-armed uracil hydrogen-bonded (H-bonded) unit was synthesized via a modular synthetic approach and characterized by H-1, C-13 NMR and MALDI-TOF mass spectroscopies. Two H-bonded tetrads, PtC-(TPAD1)(3) and PtC-(TPAD2)(3), based on a metal core PtC complexed with two generations of triarylamine dendrimers, TPAD1 and TPAD2 (with electron-donating nature), were successfully constructed with improved organic solubility via a classical H-bonded self-assembly approach. Supramolecular H-bonding in solution and solid state was elucidated by H-1 NMR titrations, IR spectral studies and time resolved photoluminescence (TRPL) measurements. The electron/energy transfers, as well as the self-assemblies of supramolecular tetrads, were established by UV-Vis and PL titrations and AFM morphological studies. Furthermore, metal complex core PtC showed selective sensitivity towards Ag+ ions through fluorescence turn-off responses without any interference from other common metal ions. The 1 : 1 binding stoichiometry and complexation mechanism between the probe and Ag+ ion was established by H-1 NMR titration. Moreover, PL reversibility of PtC + Ag+ could be achieved on addition of PMDTA.
Synthesis of novel platinum complex core as a selective Ag+ sensor and its H-bonded tetrads self-assembled with triarylamine dendrimers for electron/energy transfers
(2014-11-07)
Shellaiah, Muthaiah
;
Raju, Mandapati V. Ramakrishnam
;
Singh, Ashutosh
;
Lin, Hsin-Chieh
;
Wei, Kung-Hwa
A novel platinum complex PtC with a tri-armed uracil hydrogen-bonded (H-bonded) unit was synthesized via a modular synthetic approach and characterized by H-1, C-13 NMR and MALDI-TOF mass spectroscopies. Two H-bonded tetrads, PtC-(TPAD1)(3) and PtC-(TPAD2)(3), based on a metal core PtC complexed with two generations of triarylamine dendrimers, TPAD1 and TPAD2 (with electron-donating nature), were successfully constructed with improved organic solubility via a classical H-bonded self-assembly approach. Supramolecular H-bonding in solution and solid state was elucidated by H-1 NMR titrations, IR spectral studies and time resolved photoluminescence (TRPL) measurements. The electron/energy transfers, as well as the self-assemblies of supramolecular tetrads, were established by UV-Vis and PL titrations and AFM morphological studies. Furthermore, metal complex core PtC showed selective sensitivity towards Ag+ ions through fluorescence turn-off responses without any interference from other common metal ions. The 1: 1 binding stoichiometry and complexation mechanism between the probe and Ag+ ion was established by H-1 NMR titration. Moreover, PL reversibility of PtC + Ag+ could be achieved on addition of PMDTA.